JP2012048147A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device such as a copying machine, a facsimile, a printer or the like, which has an endless belt wound around a plurality of rollers and detection means for optically detecting an image on the belt and resolves the problems relating an assemblability, energy consumption and a down time in taking countermeasures against a curling tendency of the belt while enhancing the suppression function suppressing an occurrence of the curling tendency thereof.SOLUTION: An image forming device has: an endless belt 11 wound around a plurality of rollers 33, 72, 74 and 75; and detection means 30 for optically detecting an image on the belt 11. The plurality of rollers 33, 72, 74 and 75 comprises: the counter roller 75 opposed to the detection means 30 with the belt 11 interposed therebetween; and the other rollers 33, 72 and 74. At least the counter roller 75 of the plurality of rollers 33, 72, 74 and 75 corresponds to a region, in which the image detected by the detection means 30 is carried, in the width direction of the belt 11 and has a small diameter portion 42, of which diameter is smaller than that of an other portion 43.

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, or a printer, which has an endless belt stretched around a plurality of rollers and a detecting means for optically detecting an image on the belt.

  Conventionally, in such an image forming apparatus using an electrophotographic method or the like (see, for example, [Patent Document 1] to [Patent Document 4]), it is caused by a change in usage environment such as temperature and humidity, a change with time, and the like. Thus, there is a problem that the image density changes. For this reason, various techniques for stabilizing the image density by performing adjustment by so-called process control in such a conventional image forming apparatus have been proposed (see, for example, [Patent Document 1]). For example, a gradation pattern for density detection is created on an image carrier such as a photoconductor, the patch density is detected by an optical detection means (hereinafter referred to as an optical sensor), and toner of the gradation pattern is attached from the detected value. A method is widely used in which the amount of toner is obtained and a relational expression of the toner adhesion amount with respect to the development potential (slope: development γ, X intercept: development start voltage Vk) is used. In this method, it is always stable by changing the image forming conditions so that the target adhesion amount is obtained from the relational expression of the obtained development potential and toner adhesion amount, specifically, by changing the LD power, charging bias, and development bias. To obtain the obtained image density. Further, the toner density is changed to an appropriate value by changing the toner density control reference value as necessary.

  There are two types of optical sensors for detecting the toner adhesion amount of the gradation pattern: one that detects only regular reflection light, one that detects only diffuse reflection light, and one that detects both. It is used. These optical sensors are composed of light emitting elements such as LEDs and light receiving elements such as phototransistors. In a detection system using an optical sensor, a toner patch formed on a detection target surface is irradiated with LED light, reflected light, that is, regular reflection light or diffuse reflection light is detected by a light receiving element, and the detection result is used as a toner adhesion amount. By converting, the amount of toner adhered to the target surface is obtained.

  It is important for such an optical sensor to accurately maintain a detection distance from the detection target. This is because if the detection distance from the detection target is deviated, the sensor characteristics change, the detection accuracy is lowered, and image density control may be adversely affected. For this reason, when performing detection by an optical sensor, it is important to maintain an appropriate distance from the detection target.

  By the way, the toner patch to be detected may be carried on an endless belt such as an intermediate transfer belt. The intermediate transfer belt is usually suspended on a plurality of support rollers including a drive roller, and a considerable tension is applied so as not to cause a slip with the drive roller, and the intermediate transfer belt is in contact with the roller with a considerable winding angle. Yes. Therefore, if the state where the intermediate transfer belt is stopped and the state where the intermediate belt is in contact with the roller continues, the belt may be deformed along the curved surface of the roller at a portion where the belt is suspended from the roller. This phenomenon is called curl wrinkles, creep, etc. (hereinafter referred to as curl wrinkles). In particular, curl wrinkles are prominent when left in a high humidity environment for a long time. This is because the resin, which is the material of the belt, absorbs moisture and increases the elongation.

  The curl on the belt adversely affects the image. Specifically, a gap is generated between the photoconductor and the intermediate transfer belt at the curl wrinkle occurrence place, and the toner image is not transferred and white spots occur. As described above, in the intermediate transfer system, if the intermediate transfer belt is deformed, an abnormal image is generated immediately due to transfer failure.

  In addition, curl wrinkles also adversely affect toner adhesion amount detection by an optical sensor. Because the belt flatness is partially changed, curl wrinkles change the positional relationship between the optical sensor and the intermediate transfer belt, causing output fluctuations due to deviations in the detection distance. As a result, the image stability is lowered.

  Furthermore, the curl has an adverse effect on color misregistration correction control using specular reflection light. In addition to adjusting the image density, the process control performs color misregistration correction control that corrects color misregistration by eliminating misregistration in an image forming apparatus that forms images by superimposing different color images. However, when color misregistration correction control using specular reflection light is performed, the position of the toner image is detected by a decrease in the specular reflection light amount. As a result, the color misregistration correction control may fail due to erroneous detection of a wrinkle occurrence location as a toner image.

Various techniques related to such curl wrinkle countermeasures have been proposed.
Based on the knowledge that sensor output fluctuations due to curls and the like change according to the installation position of the optical sensor, grasp the tilt angle characteristics of the optical sensor, and the optical sensor at a position where the sensor output fluctuation is small relative to the tilt angle change. There has been proposed a technique for attaching (see, for example, [Patent Document 1]). According to this technique, even if the positional relationship (tilt angle) between the optical sensor and the belt changes due to curl wrinkles, it is considered that output fluctuation can be reduced.
However, in such a technique, since it is necessary to adjust the sensor installation angles one by one according to the angle characteristics, it takes time to install the optical sensor. In addition, since it is necessary to measure and grasp the tilt angle characteristic in advance, it takes a lot of time and cost. Furthermore, even if the position of the optical sensor is adjusted, the curl wrinkles themselves are not reduced, and thus fluctuations cannot be sufficiently suppressed.

In addition, a technology for suppressing the occurrence of curl flaws by continuously or intermittently rotating the intermediate transfer belt during standby without image formation, and in addition to this, a moisture amount detecting means for detecting the amount of environmental moisture in the vicinity of the support roller portion In a high-humidity environment in which curl wrinkles are conspicuous, a technique has been proposed in which the interval at which the intermediate transfer belt rotation operation is performed is shortened (see, for example, [Patent Document 2]). According to such a technique, even when the apparatus is left unused for a long time, it is considered that an increase in curl wrinkles at the roller winding portion can be suppressed to a certain level or less.
However, in such a technique, the power consumption increases because the main body is driven not only during the printing operation. In addition, when the machine is left unpowered for a long time, such as when the machine is transported or left in a warehouse, such a driving operation cannot be performed, and curling is prevented. I can't.

In addition, a technique for rotating the intermediate transfer belt for a predetermined time or more during warm-up or prior to image formation, and a technique for changing the predetermined time depending on the temperature and humidity detected in the apparatus have been proposed. (For example, see [Patent Document 3] and [Patent Document 4]). According to such a technique, by rotating the intermediate transfer belt for a predetermined time or more, curl wrinkles generated on the intermediate transfer belt while being left for a long time are restored to a level that does not affect image and sensor detection. Then, by performing image formation after that, it is considered that it is possible to eliminate the influence of curl wrinkles without being restricted by the material of the intermediate transfer belt.
However, in such a technique, since the intermediate transfer belt is driven until the influence of the curl wrinkle is eliminated, it takes a long adjustment time. This is not desirable from the viewpoint of reducing machine downtime. Further, power consumption increases with the drive operation.

  As described above, the conventionally proposed technologies related to curling wrinkles have problems in assembly performance, energy consumption, downtime, and the curling wrinkle suppression function itself.

  The present invention has an endless belt stretched over a plurality of rollers, and a detecting means for optically detecting an image on the belt, and assembling, energy consumption, and reduction in measures against curling of the belt. An object of the present invention is to provide an image forming apparatus such as a copying machine, a facsimile machine, and a printer which solves the problem relating to time and has an improved effect of suppressing curling.

  In order to achieve the above object, the invention according to claim 1 includes an endless belt stretched over a plurality of rollers, and a detecting means for optically detecting an image on the belt, The roller includes a counter roller facing the detection unit across the belt and another roller, and at least the counter roller of the plurality of rollers is detected by the detection unit in the width direction of the belt. The image forming apparatus has a small-diameter portion having a smaller diameter than other portions corresponding to a region where an image is carried.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, in the width direction, the width of the small diameter portion is equal to or larger than the width of the detection region of the detection means.

  A third aspect of the present invention is the image forming apparatus according to the first or second aspect, wherein a plurality of rollers having the small diameter portion among the plurality of rollers are provided, and the width of the small diameter portion is the same in the width direction. Each roller having a small diameter portion is made different from each other.

  According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the roller includes a plurality of rollers having the small-diameter portion among the plurality of rollers, and the opposing in the width direction. The width of the small diameter portion provided in the roller is smaller than the width of the small diameter portion provided in another roller.

  According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, the plurality of rollers include a plurality of rollers having the small-diameter portion, and the opposing in the width direction. The width of the small diameter part provided in a roller different from the roller is set according to the diameter of the roller.

  According to a sixth aspect of the present invention, in the image forming apparatus according to the fifth aspect, the plurality of rollers have a plurality of rollers having the small-diameter portion, and are provided on a roller different from the facing roller in the width direction. The width of the small-diameter portion is set larger as the diameter of the roller is smaller.

  According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to sixth aspects, the roller having the small-diameter portion among the plurality of rollers contacts the belt in the width direction. Between the portion and the small diameter portion, there is an inclined portion that is continuously formed in the same portion and whose diameter gradually decreases toward the small diameter portion.

  According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the first to seventh aspects, a roller that is different from the opposing roller among the plurality of rollers has the small diameter portion on condition that the diameter thereof is large or small. It is determined whether or not the small diameter portion is provided, and when the diameter is large, the small diameter portion is not provided.

  According to a ninth aspect of the present invention, in the image forming apparatus according to any one of the first to eighth aspects, a roller different from the facing roller among the plurality of rollers is provided with the small diameter portion on condition of surface elasticity. Whether or not to be provided is determined, and when the surface elasticity is large, the small diameter portion is not provided.

  The present invention includes an endless belt stretched over a plurality of rollers, and a detection unit that optically detects an image on the belt, and the plurality of rollers includes the detection unit across the belt. Each of the plurality of rollers corresponds to a region in which the image detected by the detecting means is carried in the width direction of the belt. Since the image forming apparatus has a smaller diameter part than the other parts, it is possible to maintain good detection accuracy by the detecting means by suppressing the occurrence of curl wrinkles by the small diameter part, and to curl the belt. Assembling is good in measures against wrinkles, and there is no need for air feeding operation of the belt to eliminate curl wrinkles. Im it is possible to provide an image forming apparatus excellent in use feeling of the user becomes unnecessary.

  In the width direction, if the width of the small diameter portion is set to be equal to or larger than the width of the detection area of the detection means, the occurrence of curl wrinkles by the small diameter portion is suppressed, and the curl wrinkle of the belt is also detected in the detection area. It is possible to maintain good detection accuracy by the detection means by suppressing the occurrence of disturbance factors for detection by the detection means such as or scratches and ensuring the flatness of the belt of the part detected by the detection means In addition, assembling is good in measures against curl wrinkles on the belt, and the belt air feeding operation to eliminate curl wrinkles is unnecessary, and energy consumption and downtime for this air feeding operation are unnecessary. It is possible to provide an image forming apparatus excellent in user's feeling of use.

  If there are a plurality of rollers having the small diameter portion among the plurality of rollers, and the width of the small diameter portion is made different among the rollers having the same small diameter portion in the width direction, By suppressing the occurrence of curl wrinkles, and the position of the roller that contacts the belt is shifted in the main scanning direction by each roller, the portion of the belt that can be deteriorated is shifted in the main scanning direction, and the detection accuracy by the detection means It is possible to maintain good image quality, suppress abnormal images and damage to the belt, as well as good assembly to prevent curl wrinkles on the belt and eliminate the need for belt emptying to eliminate curl wrinkles. Therefore, energy consumption and downtime for the air transport operation are unnecessary, and an image forming apparatus excellent in user's feeling can be provided.

  Among the plurality of rollers, there are a plurality of rollers having the small diameter portion, and in the width direction, the width of the small diameter portion provided in the counter roller is smaller than the width of the small diameter portion provided in another roller. If so, the detection accuracy by the detection means is kept good by suppressing the occurrence of curl wrinkles by the small-diameter portion and suppressing the occurrence of disturbance factors for detection by the detection means such as belt flapping. As a result, it is easy to assemble the belt against curl wrinkles and eliminates the need for the belt air feeding operation to eliminate curl wrinkles. It is possible to provide an image forming apparatus that is unnecessary and excellent in user experience.

  A plurality of rollers having the small-diameter portion among the plurality of rollers, and the width of the small-diameter portion provided in a roller different from the facing roller in the width direction is set according to the diameter of the roller; Then, the small diameter part whose width is set according to the diameter of the roller can make the curl wrinkle difficult even for the roller that is likely to cause the curl wrinkle. The detection accuracy by the detection means can be kept good, the assembly performance is good in measures against belt curl wrinkles, and there is no need for belt air feed operation to eliminate curl wrinkles. Therefore, it is possible to provide an image forming apparatus that eliminates the need for energy consumption and downtime, and that is excellent in user experience.

  Among the plurality of rollers, a plurality of rollers having the small-diameter portion are provided, and the width of the small-diameter portion provided in a roller different from the opposing roller in the width direction is set to be larger as the diameter of the roller is smaller. In other words, the small diameter part whose width is set in accordance with the diameter of the roller makes it difficult for the roller that is likely to cause curl wrinkles and suppresses the occurrence of curl wrinkles. It is possible to maintain good detection accuracy, as well as good assembling in measures against belt curl wrinkles, and it is not necessary to carry out the belt air feed operation to eliminate curl wrinkles. It is possible to provide an image forming apparatus that eliminates the need for energy consumption and downtime, and that provides an excellent user experience.

  Among the plurality of rollers, the roller having the small diameter portion is formed continuously between the portion in contact with the belt and the small diameter portion in the width direction and has a diameter toward the small diameter portion. If there is an inclined part that gradually decreases, the generation of curl wrinkles is suppressed by the small-diameter part, and the provision of the inclined part suppresses the occurrence of disturbance factors for detection of the detection means such as a scratch on the belt. As a result, it is possible to maintain good detection accuracy by the detection means, good assemblability in measures against belt curl wrinkles, and no belt emptying operation to eliminate curl wrinkles. It is possible to provide an image forming apparatus that eliminates the energy consumption and downtime required for the feeding operation and has an excellent user experience.

  Of the plurality of rollers, a roller different from the opposing roller is determined as to whether or not the small diameter portion is provided on condition that the diameter is large, and when the diameter is large, the small diameter portion is not included. If this is the case, it is possible to reduce the cost by omitting the small diameter portion as appropriate under the condition of the roller diameter and omitting the cost for forming the small diameter portion, and by suppressing the occurrence of curl wrinkles by the small diameter portion. In addition, it is possible to maintain good detection accuracy by the detection means, as well as good assemblability in measures against belt curl wrinkles. It is possible to provide an image forming apparatus excellent in user's feeling of use because energy consumption and downtime for operation are unnecessary.

  Of the plurality of rollers, a roller different from the facing roller is determined whether or not the small diameter portion is provided on the condition of the surface elasticity, and when the surface elasticity is large, the small diameter portion is not provided. Then, it is possible to reduce the cost by omitting the small diameter portion as appropriate under the condition of the surface elasticity of the roller and omitting the cost for forming the small diameter portion, and by suppressing the generation of curl wrinkles by the small diameter portion. In addition, it is possible to maintain good detection accuracy by the detection means, as well as good assemblability in measures against belt curl wrinkles. It is possible to provide an image forming apparatus excellent in user's feeling of use because energy consumption and downtime for operation are unnecessary.

1 is a schematic front view of an image forming apparatus to which the present invention is applied. FIG. 2 is a schematic front sectional view of a detection unit provided in the image forming apparatus shown in FIG. 1. FIG. 2 is a plan sectional view of a developing device provided in the image forming apparatus illustrated in FIG. 1. 3 is a flowchart showing a part of control related to process control performed in the image forming apparatus shown in FIG. 1. FIG. 2 is a schematic plan view showing a mode in which an image detected by a detection unit when process control is performed in the image forming apparatus shown in FIG. 1 is formed on an endless belt. 2 is a graph showing a concept used when determining image density in process control performed in the image forming apparatus shown in FIG. 1. It is the graph which showed that the output of a detection means became disordered when the curl wrinkle produced in the belt. FIG. 1 is a schematic view showing an aspect in which an image detected by the detection means when the process control is performed in the image forming apparatus shown in FIG. 1 is formed on an endless belt, and an arrangement aspect of the detection means for detecting the image. FIG. FIG. 2 is a schematic front view showing a configuration aspect of a small diameter portion provided on a roller around which an endless belt is stretched in the image forming apparatus shown in FIG. 1. It is the schematic perspective view which showed the arrangement | positioning aspect of the small diameter part shown in FIG. It is the schematic front view which showed that the width | variety of the small diameter part shown in FIG. 9 was set according to the diameter of a roller. It is the graph which showed that the output of a detection means was stabilized by the small diameter part shown in FIG. It is the schematic perspective view which showed the other arrangement | positioning aspect of the small diameter part shown in FIG.

  FIG. 1 shows an outline of an image forming apparatus to which the present invention is applied. The image forming apparatus 100 is a full-color laser printer, but may be other image forming apparatuses such as other types of printers, facsimile machines, copying machines, printing machines, and multifunction machines of copying machines and printers. The image forming apparatus 100 performs an image forming process based on an image signal corresponding to image information received from the outside. The image forming apparatus 100 can form an image using plain paper generally used for copying, OHP sheets, thick paper such as cards and postcards, and envelopes as sheet-like recording media. .

  The image forming apparatus 100 is a first image carrier capable of forming an image as an image corresponding to each color separated into yellow, magenta, cyan, and black by carrying toner as an image forming substance. A tandem structure in which photosensitive drums 20Y, 20M, 20C, and 20BK, which are photosensitive bodies as latent image carriers, are arranged in parallel, in other words, a tandem system is adopted.

  The photosensitive drums 20Y, 20M, 20C, and 20BK are endless belts that are intermediate transfer members as flexible second image carriers that are rotatably supported by a frame (not shown) of the main body 99 of the image forming apparatus 100. The transfer belt 11 as an intermediate transfer belt is a moving direction of the transfer belt 11 and is arranged in parallel at equal intervals in this order from the upstream side in the A1 direction which is the counterclockwise direction in FIG. Y, M, C, and BK added after the numerals of the respective symbols indicate members for yellow, magenta, cyan, and black.

  Each of the photosensitive drums 20Y, 20M, 20C, and 20BK is an image forming unit 60Y that is an image forming unit for forming yellow (Y), magenta (M), cyan (C), and black (BK) images. It is provided in 60M, 60C and 60BK.

  The photoconductive drums 20Y, 20M, 20C, and 20BK are positioned on the outer peripheral surface side of the transfer belt 11 that is configured as an endless belt disposed substantially at the center inside the main body 99, that is, on the image forming surface side.

  The transfer belt 11 is movable in the direction of the arrow A1 while facing the photosensitive drums 20Y, 20M, 20C, and 20BK. Visible images, that is, toner images formed on the photosensitive drums 20Y, 20M, 20C, and 20BK are respectively superimposed and transferred onto the transfer belt 11 that moves in the direction of the arrow A1, and then a sheet as a recording material that is a recording medium. The image is transferred onto the transfer paper S as a batch. Therefore, the image forming apparatus 100 is an intermediate transfer type, in other words, an indirect transfer type image forming apparatus. Therefore, the image forming apparatus 100 is a tandem indirect transfer type image forming apparatus.

  The lower portion of the transfer belt 11 faces the photosensitive drums 20Y, 20M, 20C, and 20BK, and the opposed portions transfer the toner images on the photosensitive drums 20Y, 20M, 20C, and 20BK. A primary transfer portion 58 for transferring to the transfer belt 11 is formed.

  In the superimposing transfer to the transfer belt 11, the toner images formed on the photosensitive drums 20Y, 20M, 20C, and 20BK are transferred to the same position on the transfer belt 11 while the transfer belt 11 moves in the A1 direction. As described above, by voltage application by primary transfer rollers 12Y, 12M, 12C, and 12BK as primary transfer means disposed at positions facing the respective photosensitive drums 20Y, 20M, 20C, and 20BK with the transfer belt 11 interposed therebetween, The timing is shifted from the upstream side in the A1 direction toward the downstream side.

  The transfer belt 11 has a multilayer structure in which the base layer is made of a material with little elongation, the surface of the base layer is covered with a smooth material, and the coat layer is formed on the base layer. Examples of the material of the base layer include a fluororesin, a PVDF sheet, and a polyimide resin. In this embodiment, polyimide is used. Examples of the material of the coat layer include a fluorine resin.

  Each of the transfer belts 11 has a detent guide (not shown) as a detent member at each edge thereof. The detent guide is arranged to prevent the transfer belt 11 from being biased in any of the width directions perpendicular to the paper surface in FIG. 1 corresponding to the main scanning direction when the transfer belt 11 rotates in the A1 direction. It is installed. The stopper guide is made of urethane rubber, but can be made of various rubber materials such as silicon rubber.

  The transfer belt 11 has a width corresponding to the A4-sized transfer sheet S in the width direction. Therefore, the image forming apparatus 100 can form an image on the transfer sheet S of A3 vertical size at the maximum.

  The image forming apparatus 100 is disposed in the main body 99 so as to oppose the four image forming units 60Y, 60M, 60C, and 60BK and the respective photosensitive drums 20Y, 20M, 20C, and 20BK. A transfer belt unit 10 as an intermediate transfer unit provided, a secondary transfer device 5 as a secondary transfer unit disposed on the right side of the transfer belt 11 in FIG. 1 so as to face the transfer belt 11, and an image forming unit 60Y. , 60M, 60C, 60BK, and an optical scanning device 8 serving as an exposure device as a writing unit, which is an optical writing unit serving as a latent image forming unit, arranged to face the lower side.

  The image forming apparatus 100 also serves as a paper feed cassette capable of stacking a large number of transfer sheets S conveyed toward the secondary transfer unit 57 between the transfer belt 11 and the secondary transfer apparatus 5 in the main body 99. The sheet transfer device 61 and the recording sheet S conveyed from the sheet supply device 61 are transferred at a predetermined timing in accordance with the toner image formation timing by the image forming units 60Y, 60M, 60C, and 60BK. A registration roller pair 4 that is fed out toward the registration roller 57 and a sensor (not shown) that detects that the leading edge of the transfer sheet S has reached the registration roller pair 4 are provided.

  The image forming apparatus 100 also includes a fixing device 6 as a belt-fixing type fixing unit for fixing the toner image, that is, an unfixed toner image, onto the transfer sheet S on which the toner image is transferred, and a sheet feeding device. A feeding roller (not shown) that feeds the transfer sheet S fed from the feeding device 61 is provided, a paper feed path 32 in which a registration roller pair 4 and a fixing device 6 are arranged in the middle, and a position at the end of the paper feeding path 32 Disposed on the transfer belt unit 10 is a discharge roller 7 serving as a discharge roller pair that is a discharge roller for discharging the image output product, which is the fixed transfer paper S, to the outside of the main body 99, and yellow, cyan. , Toner bottles 9Y, 9M, 9C, 9BK filled with toners of magenta and black, and a transfer disposed on the upper side of the main body 99 and discharged to the outside of the main body 99 by the discharge roller 7. And a paper discharge tray 17 as a sheet discharge unit for stacking S.

The image forming apparatus 100 also includes a driving device including a driving motor (not shown) as a driving unit (not shown) that rotates and drives the photosensitive drums 20Y, 20M, 20C, and 20BK in the main body 99, and is unnecessary due to image formation. A waste toner bottle (not shown) for storing the toner, and a control means 91 including a CPU (not shown), a memory, etc. for controlling the overall operation of the image forming apparatus 100.
The image forming units 60 </ b> Y, 60 </ b> M, 60 </ b> C, 60 </ b> BK, the transfer belt unit 10, the optical scanning device 8, and the fixing device 6 constitute an image forming unit located above the sheet feeding device 61.

  In addition to the transfer belt 11, the transfer belt unit 10 includes primary transfer rollers 12Y, 12M, 12C, and 12BK as primary transfer bias rollers, and a drive roller 72 that is a drive member around which the transfer belt 11 is wound. A counter roller 74 as a stretching roller, tension rollers 75 and 33 as support rollers for stretching the transfer belt 11 together with the driving roller 72 and the cleaning roller 74, and the transfer belt 11. And a cleaning device 13 as a belt cleaning device which is an intermediate transfer member cleaning device for cleaning the surface of the transfer belt 11.

  The transfer belt unit 10 is a toner image for process control which is disposed on the transfer belt 11 in a process control mode, which will be described later. An optical sensor 30 serving as an optical detection means for optically detecting the density detection patch, a drive system (not shown) including a drive motor (not shown) that rotationally drives the drive roller 72, and a primary transfer roller 12Y. , 12M, 12C, 12BK, a first transfer bias control means realized as one function of a power supply and a control means 91 as a first transfer bias application means (not shown) for applying a primary transfer bias independently of each other. Have.

  The driving roller 72, the cleaning counter roller 74, and the stretching rollers 75 and 33 are support rollers that are wound around the transfer belt 11 so as to be able to be rotated and conveyed. The cleaning facing roller 74 and the stretching rollers 75 and 33 are driven rollers that rotate with the transfer belt 11 that is rotationally driven by the driving roller 72. Of the support rollers 72, 74, 75, 33, only the tension roller 33 abuts on the outer peripheral surface of the transfer belt 11, and the other support rollers 72, 74, 75 are on the inner peripheral surface of the transfer belt 11. It is in contact with a certain back surface. The primary transfer rollers 12Y, 12M, 12C, and 12BK press the transfer belt 11 from the back surface thereof toward the photosensitive drums 20Y, 20M, 20C, and 20BK to form primary transfer nips. The primary transfer nip is formed in a portion of the transfer belt 11 that extends between the cleaning facing roller 74 and the stretching roller 75. The cleaning counter roller 74 and the stretching roller 75 have a function of stabilizing the primary transfer nip.

  In each primary transfer nip, a primary transfer electric field is formed between the photosensitive drums 20Y, 20M, 20C, and 20BK and the primary transfer rollers 12Y, 12M, 12C, and 12BK due to the influence of the primary transfer bias. . The toner images of the respective colors formed on the photosensitive drums 20Y, 20M, 20C, and 20BK are primarily transferred onto the transfer belt 11 due to the influence of the primary transfer electric field and nip pressure.

The driving roller 72 is in contact with the secondary transfer device 5 via the transfer belt 11 to form a secondary transfer portion 57. Therefore, the drive roller 72 also serves as a secondary transfer counter roller.
The cleaning counter roller 74 has a function as a tension roller as a pressure member that gives the transfer belt 11 a predetermined tension suitable for transfer.

  The cleaning device 13 is disposed to the left of the cleaning counter roller 74 in FIG. The cleaning device 13 is disposed so as to contact the transfer belt 11 at a position facing the cleaning counter roller 74, that is, at a position downstream of the secondary transfer portion 57 and upstream of the primary transfer portion 58 in the A1 direction. A cleaning blade 13a and a case 13b in which the cleaning blade 13a is housed.

The cleaning device 13 cleans the transfer belt 11 by scraping and removing foreign matters such as residual toner on the transfer belt 11 with a cleaning blade 13a.
The transfer belt unit 10 can be integrally attached to and detached from the main body 99.

  The optical sensor 30 is disposed outside the transfer belt 11 in the vicinity of the stretching roller 75. In this regard, the tension roller 75 is a counter roller facing the optical sensor 30 with the transfer belt 11 in between.

  As shown in FIG. 2, the optical sensor 30 includes a mounting substrate 31, an LED 36 that is mounted on the mounting substrate 31 and emits light toward the transfer belt 11 that is an irradiation target, and the LED 36 directs the transfer belt 11 toward the transfer belt 11. A regular reflection light receiving element 37 as a regular reflection light receiving means which is a light receiving means for receiving a regular reflection light of the light irradiated and reflected by the transfer belt 11, and a diffusion as a light receiving means for receiving the diffused light of the light. It has a diffuse reflected light receiving element 38 as reflected light receiving means, and a case 39 that houses the LED 36, the regular reflected light receiving element 37, and the diffuse reflected light receiving element 38 and prevents the incidence of disturbance light.

  The LED 36 is disposed between the regular reflection light receiving element 37 and the diffuse reflection light receiving element 38. The LED 36, the regular reflection light receiving element 37, and the diffuse reflection light receiving element 38 are mounted in a direction parallel to the surface direction of the substrate 31. The case 39 is molded with a black resin. A laser diode is used as the light emitting means, and a phototransistor, a photodiode, or the like is used as the light receiving means.

  The optical sensor 30 is configured to perform a calibration operation using a regular reflection light receiving element 37 that is a light receiving element. In this calibration operation, if the current value flowing through the LED 36 is increased, the light emission amount increases and the specular reflection light output detected by the specular reflection light receiving element 37 increases. Conversely, if the current value passed through the LED 36 is decreased, the light emission amount decreases. The specular reflection light output detected by the specular reflection light receiving element 37 is reduced, and the LED 36 is set so that the output value of the specular reflection light receiving element 37 falls within a predetermined range. This is an adjustment operation for adjusting the light amount of the LED 36 by changing the current to flow. Hereinafter, such calibration operation and adjustment operation are referred to as Vsg adjustment. FIG. 2 shows a state in which a density detection patch is detected during process control.

  First, when starting the Vsg adjustment, the LED 36 is turned on, and the regular reflection light receiving element 37 detects the regular reflection output value of the background portion of the transfer belt 11, that is, the portion where the toner image is not formed. Then, the current value Ifsg of the LED 36 is adjusted so that the regular reflection light output value becomes 4 ± 0.5 [V]. At this time, the current value Ifsg having the specular reflection output value closest to 4.0 [V] is detected using the binary search method. In the Vsg adjustment, the upper limit value of the current value Ifsg is set to 30 [mA]. This is a value set so that the LED 36 is not damaged.

  As a result of the binary search method, when the regular reflection output value falls within the range of 4 ± 0.5 [V], the current value Ifsg at that time is stored in the memory of the control means 91. When the regular reflection output value does not fall within the range of 4 ± 0.5 [V], Vsg adjustment fails. When this failure continues three times in succession, it is determined that an abnormality has occurred and the image forming apparatus 100 is stopped.

  However, since it takes time to adjust the Vsg, before adjusting the current value Ifsg, the background portion of the transfer belt 11 is irradiated with the light of the LED 36 for a predetermined time using the current value Ifsg at the previous Vsg adjustment. The regular reflection light is detected by the regular reflection light receiving element 37, the average value of the detected regular reflection light output is obtained, and when the average value is within a predetermined range, there is no need to adjust the current value Ifsg. Therefore, Vsg adjustment is not executed.

The sheet feeding device 61 accommodates a plurality of transfer sheets S in a state of a stack of transfer sheets, and is disposed in the lower part of the main body 99.
The sheet feeding device 61 has a feeding roller 3 as a sheet feeding roller pressed against the upper surface of the uppermost transfer sheet S, and the feeding roller 3 is driven to rotate counterclockwise at a predetermined timing. Thus, the uppermost transfer sheet S is separated one by one and fed toward the registration roller pair 4. In this respect, the paper feed roller 3 also functions as a separation roller.
The transfer sheet S delivered from the sheet feeding device 61 reaches the registration roller pair 4 through the sheet feeding path 32 and is sandwiched between the rollers of the registration roller pair 4.

  The secondary transfer device 5 is disposed to face the drive roller 72. The secondary transfer device 5 is disposed so as to sandwich the transfer belt 11 with the drive roller 72, so that the toner image on the transfer belt 11 can be transferred to the transfer paper S passing between the transfer belt 11. A secondary transfer roller 64 as a transfer member, a cleaning device (not shown) that cleans the secondary transfer roller 64, and a biasing member that biases the secondary transfer roller 64 toward the drive roller 72 And a spring (not shown).

  The secondary transfer roller 64 and a part of the transfer belt 11 near the secondary transfer portion 57 are disposed so as to face the paper feed path 32. The secondary transfer roller 64 is a second transfer bias control realized as a function of a power source and a control unit 91 (not shown) that applies a secondary transfer bias to and from the driving roller 72. Connected means.

  The power source applies to the secondary transfer roller 64 a bias having a polarity opposite to the charging polarity of the toner constituting the toner image carried on the transfer belt 11. Therefore, the secondary transfer roller 64 generates an attractive force with respect to the toner image carried on the transfer belt 11 by bias application from the power source, and electrostatically transfers the toner image onto the transfer paper S. In this respect, the secondary transfer roller 64 functions as an attractive roller.

  The fixing device 6 includes a heating roller 62 that is a hollow metal roller having a heater (not shown) therein, a fixing belt 63 wound around the heating roller 62, and a rubber member around which the fixing belt 63 is wound together with the heating roller 62. A pressure roller 69, which is a hollow roller that presses against the fixing belt 63 between the fixing roller 68 and the fixing roller 68 and forms a fixing nip 70 as a nip portion that is a pressure contact portion, and a pressure roller 69. And a heater (not shown) provided.

  The fixing device 6 also includes a tension roller 73 around which the fixing belt 63 is wound together with the heating roller 62 and the fixing roller 68, and a tension roller 73 so as to apply an urging force to the tension roller 73 in the direction of increasing the tension of the fixing belt 63. The fixing device 6 includes a spring (not shown) as a biasing member that biases the fixing belt 63 from the inside to the outside, a thermistor (not shown) as a temperature detecting means for detecting the temperature of the fixing belt 63, and the fixing device 6. And a fixing case 85 as a casing that surrounds and encloses the structure so that the structure related to the worker cannot be directly touched.

  The fixing device 6 passes the transfer paper S carrying a toner image between the fixing nips 70 so that the toner image carried on the transfer paper S is applied to the surface of the transfer paper S by the action of heat and pressure. It has become established.

  The yellow, cyan, magenta, and black toners in the toner bottles 9Y, 9M, 9C, and 9BK are polymerized toners in which the wax component is uniformly dispersed therein. Less precipitation to the outside. The toner of each color is supplied to the developing devices 80Y, 80M, 80C, and 80BK provided in the image forming units 60Y, 60M, 60C, and 60BK by a predetermined supply amount through a conveyance path (not shown).

  The image forming units 60Y, 60M, 60C, and 60BK have the same configuration. The image forming units 60Y, 60M, 60C, and 60BK are primarily transferred as image forming means around the photosensitive drums 20Y, 20M, 20C, and 20BK along the rotation direction B1 that is clockwise in FIG. Rollers 12Y, 12M, 12C, and 12BK, cleaning devices 71Y, 71M, 71C, and 71BK that are cleaning devices as cleaning means, a static elimination device that is not shown as static elimination means, and charging that performs AC charging to form a charging bias There are charging devices 79Y, 79M, 79C, 79BK as charging means provided with rollers 51Y, 51M, 51C, 51BK, and developing devices 80Y, 80M, 80C, 80BK as developing means for developing with two-component developer. is doing.

  As shown in FIG. 1 or FIG. 2, the developing devices 80Y, 80M, 80C, 80BK are developing rollers 76Y, 76M as developer carrying members disposed so as to face the photosensitive drums 20Y, 20M, 20C, 20BK. , 76C, 76BK, and first screws 65Y, 65M, 65C, 65BK and second screws 66Y, 66M, 66C, 66BK, which are biaxial screws that stir while conveying the developer.

  The developing devices 80Y, 80M, 80C, and 80BK also include a developer chamber (not shown) that houses the first screws 65Y, 65M, 65C, and 65BK, the second screws 66Y, 66M, 66C, and 66BK, and the second screws 66Y and 66M, respectively. , 66C, 66BK, toner density sensors 67Y, 67M, 67C, 67BK as toner density detection sensors that are located below the developer chambers and that detect the toner density in the developer.

  The developing devices 80Y, 80M, 80C, and 80BK also serve as toner replenishing means that replenishes toner in the toner bottles 9Y, 9M, 9C, and 9BK into the apparatus main body according to the output of the toner density sensors 67Y, 67M, 67C, and 67BK. A toner replenishing device (not shown), toner replenishing ports 77Y, 77M, 77C, and 77BK that receive toner replenished by the toner replenishing device, developing rollers 76Y, 76M, 76C, and 76BK, and photosensitive drums 20Y, 20M, 20C, and 20BK. And a bias applying means (not shown) for applying a developing bias to the developing area between the two.

  The first screws 65Y, 65M, 65C, 65BK and the second screws 66Y, 66M, 66C, 66BK circulate and convey the developer in the developer chamber. The first screws 65Y, 65M, 65C, and 65BK pump the developer to the developing rollers 76Y, 76M, 76C, and 76BK, and carry them on the developing rollers 76Y, 76M, 76C, and 76BK. The developer carried on the developing rollers 76Y, 76M, 76C, and 76BK passes on the surface of the photosensitive drums 20Y, 20M, 20C, and 20BK when passing through the developing area as the developing rollers 76Y, 76M, 76C, and 76BK rotate. The electrostatic latent image formed as described later is developed with toner. The developer that has passed through the development area is returned to the developer chamber.

  The toner concentration sensors 67Y, 67M, 67C, and 67BK measure the toner permeability, and output the measurement result to the control unit 91. The control means 91 compares the output value Vt of the toner density sensors 67Y, 67M, 67C and 67BK with the control reference value Vtref of the toner density, and stores the amount of toner to be replenished according to the difference, that is, the toner replenishment amount in its memory. And the toner supply device is driven to supply the calculated amount of toner into the developer chamber through the toner supply ports 77Y, 77M, 77C, and 77BK.

  The image forming units 60Y, 60M, 60C, and 60BK can be pulled out from the main body 99 along guide rails (not shown) fixed to the main body 99, and can be pushed into the main body 99. In contrast, the process cartridge is detachably installed. When the image forming units 60Y, 60M, 60C, and 60BK as process cartridges are pushed into the main body 99, they are loaded and positioned at predetermined positions suitable for image formation. Making a process cartridge in this way is very preferable because it can be handled as a replacement part, so that the maintainability is remarkably improved. In addition, since the life of each part, which is an element of the process cartridge, is equal, unnecessary replacement is prevented and suppressed, and the structure is further preferable.

  In the image forming apparatus 100 having such a configuration, when a signal indicating that a color image should be formed is input by the user, printing including image information corresponding to a full-color image that is a desired image to be formed by the control unit 91 is performed. The image forming job, which is a job, is stored and held in the memory, the driving roller 72 is driven, the transfer belt 11, the cleaning facing roller 74, and the stretching rollers 75 and 33 are driven to rotate, and the photosensitive drums 20Y and 20M are driven. , 20C, 20BK are rotationally driven in the B1 direction.

  As the photosensitive drums 20Y, 20M, 20C, and 20BK are rotated in the B1 direction, the surfaces of the photosensitive drums 20Y, 20M, 20C, and 20BK are uniformly charged to a predetermined polarity by the charging bias by the charging devices 79Y, 79M, 79C, and 79BK. The exposure scans or irradiations of light-modulated laser light directed upward in the main scanning direction, which approximately coincides with the vertical direction of the drawing in FIG. 1, correspond to the respective colors of yellow, magenta, cyan, and black. A latent image corresponding to the image information is formed by the electrostatic latent image, and the electrostatic latent image is subjected to toners of yellow, magenta, cyan, and black by developing biases of developing devices 80Y, 80M, 80C, and 80BK and toner charging. Is developed and visualized to form a single-color image composed of toner images of magenta, cyan, and black.

  Note that the control unit 91 decomposes the image information stored in the memory into color information of each color of yellow, magenta, cyan, and black when driving the optical scanning device 8 to form an electrostatic latent image corresponding to each color. The optical scanning device 8 is driven based on each color image information which is monochromatic image information separated into each color.

  The yellow, magenta, cyan, and black toner images obtained by development are sequentially from the yellow toner image located on the most upstream side in the A1 direction, in the order of a magenta toner image, a cyan toner image, and a black toner image. The primary transfer bias formed by the primary transfer rollers 12Y, 12M, 12C, and 12BK is primarily transferred to the same position on the transfer belt 11 rotating in the A1 direction to perform color superposition. A composite color image, which is a full-color toner image, is formed and carried thereon.

  On the other hand, when a signal indicating that a color image should be formed is input, the feeding roller 3 provided in the sheet feeding device 61 rotates to feed out the transfer sheet S and separate the sheets one by one into the sheet feeding path 32. The transfer sheet S fed in and fed into the paper feed path 32 is further transported by a transport roller (not shown) and stops in a state where it abuts against the registration roller pair 4.

  In accordance with the timing at which the composite color image superimposed on the transfer belt 11 moves to the secondary transfer portion 57 as the transfer belt 11 rotates in the A1 direction, in other words, the sheet feeding timing is measured, and the registration roller pair 4 The secondary color transfer unit 57 is in close contact with the transfer sheet S sent to the secondary transfer unit 57, and the combined transfer image is applied to the transfer sheet S by the action of the secondary transfer bias and the nip pressure. Next transferred and recorded.

  The transfer sheet S is transported by the secondary transfer device 5 and fed into the fixing device 6, and when passing through the fixing nip 70, that is, the fixing portion between the fixing belt 63 and the pressure roller 69 in the fixing device 6, heat and pressure are transferred. As a result, the carried toner image, that is, the synthesized color image is fixed.

  The transfer sheet S on which the composite color image has been fixed, which has passed through the fixing device 6, is discharged out of the main body 99 through the discharge roller 7 and stacked on the discharge tray 17 at the top of the main body 99.

  The photosensitive drums 20Y, 20M, 20C, and 20BK are cleaned by removing residual transfer toner, which is residual toner that remains after transfer, and becomes unnecessary toner, by wiping it from the surface with the cleaning devices 71Y, 71M, 71C, and 71BK. The charge is removed by the device, the surface potential is initialized, and the next charging is performed by the charging devices 79Y, 79M, 79C, and 79BK. Transfer residual toner removed from the surfaces of the photosensitive drums 20Y, 20M, 20C, and 20BK by the cleaning devices 71Y, 71M, 71C, and 71BK is stored in a waste toner bottle.

  The transfer belt 11 that has passed through the secondary transfer portion 57 after the secondary transfer is wiped off untransferred residual toner that is unnecessary toner remaining on the surface after the transfer by the cleaning blade 13a provided in the cleaning device 13, Removed and cleaned to prepare for the next transfer. The transfer residual toner removed from the surface of the transfer belt 11 by the cleaning device 13 is stored in a waste toner bottle.

  In addition to the image forming mode in which the user-specified image formation is performed in this manner, the image forming apparatus 100 performs process control in order to optimize the image density of each color when the power is turned on or after a predetermined number of sheets have passed, that is, after image formation. It has a process control mode in which operations are performed. In this process control operation, a density detection patch as a gradation pattern of each color is formed on the transfer belt 11 by sequentially switching a charging bias and a developing bias at an appropriate timing, and these gradation patterns are optically formed. Detected by the sensor 30, the output voltage is converted into an adhesion amount, and the development γ and development start voltage Vk representing development capability are calculated. Based on the calculated values, the development bias value and the toner density control target value are changed. Control to do.

The contents of the process control operation will be described with reference to FIG.
(1) Device startup (step S1)
When the image forming apparatus 100 is turned on, the bias of various motors and various devices is turned on when a predetermined number of sheets are printed, and preparations for executing process control are performed.

(2) Vsg adjustment (step S2)
Vsg adjustment is performed as described above. That is, the LED 36 is turned on, the regular reflection output value of the background portion of the transfer belt 11 is detected by the regular reflection light receiving element 37, and the regular reflection light output value of the LED 36 is 4 ± 0.5 [V]. Adjust the current value. Ifsg with the specular reflection output value closest to 4.0 [V] is detected using the binary search method.

(3) The outputs (Vt) of the toner density sensors 67Y, 67M, 67C, and 67BK are acquired in the developing devices 80Y, 80M, 80C, and 80BK, respectively (step S3). This is measured in order to know the toner density at the time of detection, and is necessary for correcting a toner density control reference value (Vtref) described later.

(4) Creation of gradation pattern (step S4)
This is necessary for detecting the development γ. Specifically, as shown in FIG. 5, the width 10 [mm] in the main scanning direction and the sub-scanning correspond to the position where the optical sensor 30 is provided. A gradation pattern is formed by forming a density detection patch with a direction width of 14.4 [mm] and a pattern interval of 5.6 [mm]. The main scanning direction coincides with the width direction of the transfer belt 11, and the sub-scanning direction is a direction parallel to the A1 direction and orthogonal to the main scanning direction. As shown in the figure, the optical sensor 30 has a center that is the center in the main scanning direction and a front and a rear that are the respective ends in the main scanning direction. A total of three are arranged so as to face each other. Reference numeral 49 denotes a support plate that is a support member as a detection means support member that integrally supports the optical sensors 30.

  It is desirable that the number of density detection patches for each color to be created be a number that fits in the pitch between drums. The inter-drum pitch is a distance between the photosensitive drums 20Y, 20M, 20C, and 20BK, and image formation such as writing by the optical scanning device 8 is started simultaneously on each of the photosensitive drums 20Y, 20M, 20C, and 20BK. In this case, the leading edges of the images formed on the photosensitive drums 20Y, 20M, 20C, and 20BK coincide with each other on the transfer belt 11.

  The number of density detection patches for each color to be created is the number that fits in the pitch between drums. If the total length of the gradation pattern for each color to be created is longer than the pitch between drums, it will overlap with other colors. After that, the writing delay must be performed, and the writing of the next color gradation pattern must be started after waiting for the creation of the gradation pattern for the other colors. This is because it takes a long time to complete the generation of the gradation pattern, and the time required for the adjustment operation becomes long.

In this embodiment, since the pitch between the drums is 100 [mm], the maximum number of gradation patterns that can be accommodated in the pitch between the drums is
(Drum pitch 100 [mm]) / (Width in pattern sub-scanning direction: 14.4 [mm] + pattern interval: 5.6 [mm]) = 5
Thus, a toner patch is created with 5 or less patches for each color.

  In writing the pattern formation, the exposure amount is set to a value at which full exposure is performed, that is, the photosensitive drums 20Y, 20M, 20C, and 20BK are sufficiently neutralized, and the gradation pattern is changed by changing the development bias and the charging bias for each pattern. create.

(5) The gradation pattern is detected by the optical sensor 30 (step S5).
Each density detection patch formed on each of the photosensitive drums 20Y, 20M, 20C, and 20BK and transferred to the transfer belt 11 is detected by the optical sensor 30, and the toner adhesion amount is obtained. For the C, M, and Y gradation patterns, the specular reflection light receiving element 37 and the diffuse reflection light receiving element 38 detect both the specular reflection light and the diffuse reflection light, and the Bk gradation pattern is a specular reflection light. Only the regular reflection light is detected by the light receiving element 37.

  However, the density detection pattern, which is a density detection patch, is detected by one optical sensor 30 arranged in the center, and the gradation pattern of all colors is detected by this optical sensor 30. The optical sensor 30 installed at the front and rear positions is used to perform positional deviation correction control for the purpose of color misregistration correction control and the like.

(6) Obtain development γ and development start voltage Vk (step S6).
The development γ and the development start voltage Vk are obtained from the relationship between the development potential when the toner patch, which is a density detection patch, is formed and the toner adhesion amount obtained in step S5. Specifically, as shown in FIG. 6, the horizontal axis represents the development potential, the vertical axis represents the toner adhesion amount, and a linear equation is obtained by the least square method. The slope of the linear equation is defined as development γ, and the X-intercept is defined as the development start voltage Vk.

(7) A developing bias necessary for obtaining the target toner adhesion amount is obtained (step S7).
Based on the linear equation obtained in step S6, the development potential on the horizontal axis corresponding to the target adhesion amount on the vertical axis is obtained. The target adhesion amount is determined in advance as a value necessary for obtaining the top concentration, and is determined by the coloring degree of the toner pigment and the toner particle diameter. cm ^ 2].

  The developing bias value obtained here is set as developing bias Vb of the developing devices 80Y, 80M, 80C, and 80BK. The charging bias: Vc is determined in advance with a value such that carriers in the developer in the developing devices 80Y, 80M, 80C, and 80BK do not fly to the photosensitive drums 20Y, 20M, 20C, and 20BK. Vb = 400 to 750 [−V] and Vc = Vb + 100 to 200 [−V] are generally used. The Vb and Vc thus determined are set as the developing bias and charging bias at the time of image formation.

(8) The toner density control reference value Vtref is corrected (step S8).
The toner density control reference value Vtref is corrected from the development γ and the toner density sensor output Vt. That is, Δγ = development γ detection value−development γ target value is obtained. Here, the development γ target value is determined in advance for each apparatus, and is, for example, 1.0 [mg / cm 2 / kV]. This value indicates that 1.0 [mg / cm ^ 2] of toner with a development potential of 1000 [V] (1 [kV]) adheres to the photosensitive drums 20Y, 20M, 20C, and 20BK, and development starts. If the voltage is 0 V and the target toner adhesion amount is 0.5 [mg / cm ^ 2], a development potential of 500 [V] is required.

  Since development potential = | Vb−Vl |, when Vl = 50 [−V], Vb = 550 [−V]. V1 represents a post-exposure potential, and depends on the photoconductor characteristics since it is a photoconductor potential when fully exposed. If Δγ exceeds a predetermined value, Vb exceeds a settable range or an abnormal image occurs. Therefore, the toner density control reference value Vtref is corrected so that Δγ becomes the target range. However, no correction is made when Vt at this time is significantly different from Vtref.

An example of correction will be shown.
-Correction condition 1:
When Δγ ≧ 0.30 [mg / cm ^ 2 / kV] (high) and Vt−Vtref ≧ −0.2 [V], Vtref = Vt−0.2 [V]. That is, the control reference value is set so as to lower the toner density from the current time.
-Correction condition 2:
When Δγ ≦ 0.30 [mg / cm ^ 2 / kV] (low) and Vt−Vtref ≦ 0.2 [V], Vtref = Vt + 0.2 [V]. That is, the control reference value is set so as to increase the toner density from the current time.
Other than the correction condition 1 and the correction condition 2, Vtref = previous value.

The curl wrinkles of the transfer belt 11 will be described.
An intermediate transfer unit having the same configuration as that of the transfer belt unit 10 is left in a high humidity environment for a long time, and the belt similar to the transfer belt 11 is driven using this intermediate transfer unit. FIG. 7 shows the measured sensor output of the belt background. From the figure, it can be seen that the sensor output fluctuates greatly in part. The portion where the sensor output greatly fluctuates is a result when the optical sensor detects a portion where the curl wrinkle is generated. When curl wrinkles occur in the belt as described above, the sensor output fluctuates as a result of the detection distance between the optical sensor and the detection target being shifted due to the influence. Therefore, when curl occurs, the detection accuracy of the density detection patch or gradation pattern decreases, and stable image density control cannot be performed even if process control is performed.

Therefore, the transfer belt unit 10 employs the following configuration in order to reduce such sensor output fluctuations due to curl wrinkles.
As shown in FIG. 8, the transfer belt 11 includes, in the width direction, an area MA as a toner pattern forming area where a toner pattern constituting a density detection patch and a gradation pattern is formed, and a toner other than the area MA. And an area MB as a pattern non-formation area. These areas MA and MB are formed so as to occupy the same position in the width direction of the transfer belt 11 over the entire circumference of the transfer belt 11.

  As described above, the optical sensor 30 measures the transfer belt 11 so that the center as the center in the main scanning direction and the front and rear as the respective ends in the main scanning direction are opposed to each other. Although three are arranged, the area MA is located at the center of the transfer belt 11 in the center in the main scanning direction and the front and rear of each end in the main scanning direction. Because. Each optical sensor 30 is arranged corresponding to each area MA in the main scanning direction. Therefore, the area MA is an area in which a toner pattern, which is an image detected by the optical sensor 30, is carried in the width direction of the transfer belt 11.

  In FIG. 9A, the area MA is indicated by a broken line only for Front as a representative example, but in reality, there are areas MA for Center and Rear as shown in FIG. Further, the shapes of the driving roller 72, the cleaning facing roller 74, and the stretching rollers 75 and 33 shown in FIG. In FIG. 5B, the drive roller 72, the cleaning facing roller 74, and the stretching rollers 75 and 33, which are support rollers, are not shown.

  FIG. 9 shows the relative positional relationship among the driving roller 72, the cleaning opposing roller 74, the stretching rollers 75 and 33, the optical sensor 30, and the transfer belt 11, which are support rollers. In the drawing, reference numeral 41 denotes other rollers which are rollers except the support roller 75 which is a counter roller among the support rollers. Therefore, the tension roller 75 is shown only in FIG. 5A, and the other roller 41 is shown in FIG.

  As shown in the figure, the tension roller 75 and the other rollers 41 have a small diameter portion 42 that is smaller in diameter than the other portions and spaced from the back surface of the transfer belt 11 corresponding to the region MA. In addition, corresponding to the region MB, as other portions, the basic diameter portion 43 that is larger in diameter than the small diameter portion 42 and is in contact with the back surface of the transfer belt 11 is located between the small diameter portion 42 and the basic diameter portion 43. The small-diameter portion 42 and the basic-diameter portion 43 have an inclined portion 44 that is formed smoothly and continuously without a step and whose diameter gradually decreases toward the small-diameter portion 42.

  The diameter d1 of the small diameter portion 42 of the stretching roller 75 corresponding to the region MA is set to be smaller than the diameter D1 of the basic diameter portion 43 of the stretching roller 75 corresponding to the region MB, and other rollers corresponding to the region MA. The diameter d2 of the small diameter portion 42 of 41 is set to be smaller than the diameter D2 of the basic diameter portion 43 of the other roller 41 corresponding to the region MB.

  As described above, portions of the stretching roller 75 and the other rollers 41 corresponding to the region MA are formed in a concave shape to form the small diameter portion 42. The depth w1 at which the roller diameter is set to be small is a depth at which the contact of the transfer belt 11 with the tension roller 75 and the small diameter portion 42 of the other rollers 41 is reliably avoided. mm]. For this reason, the back surface of the portion corresponding to the region MA of the transfer belt 11 is configured not to contact the circumferential surface of the stretching roller 75 and the other rollers 41. As a result, the tension applied to the transfer belt 11 by winding around the stretching roller 75 and other rollers 41 in the area MA is the tension applied to the transfer belt 11 by winding around the stretching roller 75 and other rollers 41 in the area MB. Since it becomes smaller than that, the transfer belt 11 is difficult to curl at a portion corresponding to the small diameter portion 42 in the width direction, that is, a portion corresponding to the region MA.

  The inclined portion 44 is formed by chamfering the end portion, that is, the edge of the basic diameter portion 43 in the manufacturing process, and the surface thereof is a cut surface. By providing the inclined portion 44 by chamfering in this way, it is possible to prevent the edge portion of the basic diameter portion 43 from rubbing against the back surface of the transfer belt 11 and causing damage to the transfer belt 11. In particular, when the transfer belt 11 is left in a high humidity environment for a long time, a vertical streak-shaped belt wrinkle may occur in the sub-scanning direction at a position corresponding to the edge portion. However, by forming the inclined portion 44, Even in such a case, curl wrinkles and belt wrinkles are less likely to occur. The inclined portion 44 is formed so that the cut surface forms a straight line in a cross section parallel to the main scanning direction, but may be formed so as to form a curved surface. In this case, the cut surface particularly has a convex shape. Such a configuration is preferable because it smoothly and smoothly continues with the basic diameter portion 43. The inclined portion 44 only needs to be continuous with at least the basic diameter portion 43. Between the small diameter portion 42 and the small diameter portion 42, the inclined portion 44 has a diameter smaller than that of the basic diameter portion 43 and smaller than that of the basic diameter portion 43. A portion separated from the center may be interposed.

  As shown in FIG. 10, in all the rollers 72, 74, 75, and 33 on which the transfer belt 11 is suspended, the roller diameter corresponding to the area MA, that is, the diameters d1 and d2 of the small diameter portion 42 are set in the area MB. In order to make it smaller than the corresponding roller diameter, that is, the diameters D1 and D2 of the basic diameter portion, curl wrinkles are suppressed in the portions corresponding to the area MA in all the rollers 72, 74, 75, and 33. The output fluctuation of the optical sensor 30 is reduced for all the positions, that is, over the entire circumference of the transfer belt 11.

  For example, as a technique for preventing a phenomenon in which noise appears in the output of the optical sensor 30 due to dust or the like being caught between the stretching roller 75 and the back surface of the transfer belt 11, the optical sensor 30 is disposed oppositely. When the configuration in which the small-diameter portion 42 is provided only on the tension roller 75 that is a counter roller, the influence of curl wrinkles generated on the tension roller 75 can be reduced as a secondary function. The curl generated at 41 is not reduced at all (except when the other rollers 41 have a large diameter or a large surface elasticity, as will be described later). As a result, when the curl generated by the other roller 41 moves to the position facing the optical sensor 30 by driving the transfer belt 11, the output fluctuation of the optical sensor 30 occurs.

  On the other hand, by providing the small-diameter portion 42 corresponding to the region MA in all the rollers 72, 74, 75, 33 that suspend the transfer belt 11, curl wrinkles are suppressed over the entire circumference of the transfer belt 11. Thus, the output fluctuation is greatly suppressed, and the change in the positional relationship between the optical sensor 30 and the transfer belt 11 is suppressed. Therefore, in the center optical sensor 30, the density detection of the toner pattern constituting the gradation pattern can be accurately maintained, the process control is performed well, the image density is stabilized over time, and the image formation is good. Is done. Further, in the front and rear optical sensors 30, positional deviation correction control for the purpose of color misregistration correction control and the like is performed satisfactorily, and color misregistration and image formation position deviation are suppressed, and good image formation is performed. Is called. The above is realized more highly by providing the inclined portion 44.

  In FIG. 10, for easy understanding of the shapes of the rollers 72, 74, 75, and 33, the drawing is performed with the transfer belt 11 seen through. Further, the shapes and sizes of the rollers 72, 74, 75, and 33 are schematically shown. The illustration of the inclined portion 44 is omitted, and the positions and diameters of the small-diameter portion 42 and the basic shape portion 43, The width is not always accurate. The same applies to FIG. In the other drawings, the shapes and sizes of the rollers 72, 74, 75, and 33 are schematically shown, and the positions and sizes of the respective parts are not necessarily accurate.

  In the width direction of the transfer belt 11, the widths of all the small diameter portions 42 formed on the rollers 72, 74, 75, and 33 are set to be equal to or larger than the width of the detection area by the optical sensor 30. The detection area width of the optical sensor 30 is the spot diameter of the optical sensor 30, that is, the irradiation diameter of light formed on the surface of the transfer belt 11 by the light irradiated by the LED 36, the regular reflection light receiving element 37, and the diffuse reflection light receiving element 38. The width of the range that can be detected by the optical sensor 30, specifically, the specular reflection light receiving element 37 and the diffuse reflection light receiving element 38, that is, the effective detection width.

  If the width of the small-diameter portion 42 is set to be smaller than the detection region width, a portion in which the curl wrinkle is generated within the detection range of the optical sensor 30 and output fluctuation of the optical sensor 30 may occur. Further, if the above-described vertical stripe-shaped belt wrinkle occurs, the belt wrinkle portion enters the detection range of the optical sensor 30, and the detection cannot be performed stably. In particular, when the width L1 (see FIG. 9) of the small-diameter portion 42 of the tension roller 75, which is a counter roller, is set to be smaller than the detection region width, the surface of the transfer belt 11 corresponding to the edge portion of the basic diameter portion 43 is detected by the optical sensor. 30, the flatness of the surface to be detected by the optical sensor 30 tends to be unstable, and stable detection may not be performed. Therefore, in order to perform stable detection, among the rollers 72, 74, 75, and 33 that are support rollers, at least the width L1 of the small-diameter portion 42 of the stretching roller 75 that is a counter roller is set to be equal to or greater than the detection region width.

  The widths of the small-diameter portions 42 provided on the rollers 72, 74, 75, and 33, which are the support rollers, corresponding to the same area MA are all different from each other in the rollers 72, 74, 75, and 33. . When the width of the small-diameter portion 42 is the same, the edge portion of the basic diameter portion 43 and the back surface of the transfer belt 11 are always in the same position in the width direction of the transfer belt 11 in each of the rollers 72, 74, 75, and 33. Therefore, the transfer belt 11 is easily scratched along the sub-scanning direction, and problems such as generation of abnormal images and breakage of the transfer belt 11 may occur. However, if the width of the small diameter portion 42 is set to a different length for each of the rollers 72, 74, 75, 33, the position where the edge portion of the basic diameter portion 43 and the back surface of the transfer belt 11 are in contact with each other is the roller 72, Since each of 74, 75, and 33 is displaced, such a problem is less likely to occur.

  In this case, it is desirable that the width L1 of the small-diameter portion 42 provided on the stretching roller 75 that is the opposing roller is the narrowest compared with the width L2 (see FIG. 9) of the small-diameter portion 42 of the other rollers 41. 100 is like that. If the width L1 of the small diameter portion 42 provided on the stretching roller 75 is set large, the non-contact portion between the transfer belt 11 and the stretching roller 75 is enlarged. As a result, the belt tends to sag at the non-contact portion, and when the transfer belt 11 is driven to rotate, in other words, a wobbling phenomenon may occur. This phenomenon does not matter even if it occurs in a portion that is wound around another roller 41. However, if this phenomenon occurs in a portion that is wound around a tension roller 75 that is a counter roller, such waviness and fluttering are Noise is generated in the output waveform of the sensor 30 and the detection accuracy is lowered.

  However, the width L1 of the small-diameter portion 42 provided in the tension roller 75 that is the opposite roller is the narrowest compared with the width L2 (see FIG. 9) of the small-diameter portion 42 of the other rollers 41, and thus this phenomenon is caused. The output fluctuation of the optical sensor 30 is suppressed, and at the same time, even if the transfer belt 11 is damaged at the portion corresponding to the edge portion of the basic diameter portion 43, the portion corresponding to the scratch is detected by the optical sensor 30. By not entering the region, more stable detection is performed. However, the width L1 of the small-diameter portion 42 provided on the stretching roller 75 that is the opposing roller is equal to or larger than the detection width of the optical sensor 30.

  The width L2 of the small diameter portion 42 in the other roller 41 is set according to the diameter, specifically the diameter D2. More specifically, the width L2 is set larger as the diameter D2 is smaller. The reason for this will be described below. The curl wrinkles occur more strongly as the diameter D2 is smaller. This is because, as the diameter D2 of the transfer belt 11 is smaller, the transfer belt 11 is wound around by the roller, and the force applied to the transfer belt 11 is increased and is easily deformed. For this reason, it is necessary to set the width L2 such that the smaller the diameter D2, the harder it is to curl. On the other hand, when the width L2 is increased, a non-contact portion between the transfer belt 11 and the roller 41 is increased, so that the force with which the transfer belt 11 is pulled by the roller 41 is reduced, and the extension amount of the transfer belt 11 is reduced. As a result, the transfer belt 11 is less likely to be curled and the output fluctuation of the optical sensor 30 is reduced.

  Therefore, the width L2 of the small diameter portion 42 in the other rollers 41 is set to be larger as the diameter D2 is smaller. As a result, it is possible to make the curl wrinkles difficult even with a roller that is likely to generate strong curl wrinkles.

  This is illustrated in FIG. This figure is a partial front view of the other roller 41 and the transfer belt 11, and shows the setting of the width L2 of the small diameter portion 42 with respect to the diameter D2 of the other roller 41. As can be seen from a comparison between FIG. 4A and FIG. 4B, when the diameter D4 is smaller than the diameter D3, the width L4 of the small diameter portion 42 is set larger than the width L3. Thus, by changing the width L2 according to the diameter D2, it becomes possible to make it difficult to curl.

  FIG. 12 shows a case where the present method, that is, the case where the small diameter portion 42 is provided, and a case where the conventional method, ie, the case where only the basic diameter portion 43 is provided and the small diameter portion 42 is not provided, leave the transfer belt 11 in a high humidity environment for a long time. The result of curling the transfer belt 11 and detecting it with the optical sensor 30 is shown. In the figure, the waveforms are offset and displayed so that the present method and the conventional method are easy to see. The small diameter portion 42 is provided in all of the rollers 72, 74, 75, and 33 that are support rollers.

  As can be seen from the figure, when this method is used, the influence of curl wrinkles is small at all positions on the entire circumference of the transfer belt 11, and the output fluctuation of the optical sensor 30 is reduced. Thus, when the small diameter part 42 is provided, the influence by a curl wrinkle is suppressed.

  In the above description, the small diameter portion 42 is provided in all of the rollers 72, 75, and 33 that are the other rollers 41. However, in the following cases, the rollers 72, 75, and 33 that are the other rollers 41 are not necessarily provided. It is not necessary to provide the small diameter part 42 in all. For example, the transfer belt 11 is suspended by a plurality of rollers 72, 74, 75, and 33 that are support rollers, but the rollers 72, 75, and 33 that are the other rollers 41 have a large diameter or a metal roller. A material coated with a low elastic modulus material such as rubber may be used. When the diameters of the rollers 72, 74, 75, and 33 that are support rollers are sufficiently large, the angle at which the transfer belt 11 wraps around these rollers 72, 74, 75, and 33 is small, and the force applied to the transfer belt 11 is small. . Further, when a material having a low elastic modulus is coated, the force applied to the transfer belt 11 is reduced because the coat layer is deformed.

  Therefore, among the plurality of rollers 72, 74, 75, and 33 that are support rollers, the rollers 72, 75, and 33 that are other rollers 41 that are different from the tension roller 75 that is a counter roller, Whether or not to provide the small-diameter portion 42 is determined on the condition that the surface elasticity is large. If the diameter is large, the small-diameter portion 42 may not be provided when the surface elasticity is large. For the driving roller 72 that is a counter roller, a small-diameter portion 42 is provided in order to suppress output fluctuation of the optical sensor 30.

  A specific example is shown in FIG. In this example, the diameter of the driving roller 72 which is the other roller 41 is sufficiently large, and the influence of curl wrinkles is small even if the portion corresponding to the region MA is not made small. Therefore, the small diameter portion 42 is not provided for the driving roller 72. Similarly, a roller coated with a material having a low elastic modulus is less affected by curl wrinkles, and therefore may not have a small diameter portion. Of course, it is also possible to provide a small-diameter portion so that the influence of curl wrinkles becomes smaller. How large the diameter is and how large the surface elasticity is to not provide the small diameter portion 42 is a matter appropriately determined by the material of the transfer belt 11 and the like. Further, as a condition for determining whether or not to provide the small-diameter portion 42, either one of the diameter and the surface elasticity may be used. When both of these are used, the degree of the diameter and the surface In consideration of the balance with the degree of elasticity, whether or not to provide the small-diameter portion 42 is appropriately determined according to the combination.

  As described above, even if the plurality of rollers 72, 74, 75, and 33 that are the support rollers are used, the rollers 72, 74, and 33 that are the other rollers 41 that are different from the stretching roller 75 that is the opposed roller 42 may not be provided. In other words, the stretching roller 75 that is at least the counter roller among the plurality of rollers 72, 74, 75, and 33 that are the support rollers has the small diameter portion 42.

  Further, as described above, the width of the small-diameter portion 42 is made different when a plurality of the rollers 72, 74, 75, and 33 that are support rollers have the small-diameter portion 42, that is, a stretching roller that is a counter roller. In this case, the small diameter portion 42 is provided in addition to 75. Similarly, it is also possible to make the width L1 of the small-diameter portion 42 provided in the stretching roller 75 that is the opposing roller smaller than the width L2 of the small-diameter portion 42 provided in the other rollers 41, the roller 72 that is the support roller, This is a case where a plurality of 74, 75, and 33 have the small diameter portion 42, that is, a case where the small diameter portion 42 is provided in addition to the stretching roller 75 that is a counter roller. Further, the width L2 of the small-diameter portion 42 provided in the other roller 41 is set according to the diameter D2 of the roller. The small-diameter portion is set in at least one of the rollers 72, 75, and 33 that are the other rollers 41. 42 is provided.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the specific embodiments, and the present invention described in the claims is not specifically limited by the above description. Various modifications and changes are possible within the scope of the above.

  For example, it is only necessary that at least one roller that spans the endless belt is provided in addition to the opposing roller. The endless belt may be a member that forms an electrostatic latent image such as a photosensitive member instead of an intermediate transfer member as long as an image on the belt is optically detected by a detecting unit. The endless belt is a member that functions as an image carrier in that it carries an image optically detected by the detection means. The image carried by the image carrier may be an image formed of another image forming material such as ink instead of a toner image.

  If these conditions are satisfied, an image forming apparatus to which the present invention is applied can adopt a direct transfer method instead of the indirect transfer method described above, even if it is a tandem type. The image forming apparatus is not a so-called tandem type image forming apparatus, but a so-called one-drum type image forming apparatus that sequentially forms toner images of respective colors on a single photosensitive drum and sequentially superimposes the color toner images to obtain a color image. The intermediate transfer member can be applied to the image forming apparatus in the same manner, and in addition, the toner image of each color is developed on an image carrier such as a sheet-like organic photoreceptor, but the color superposition itself is separate. The present invention can also be applied to image forming apparatuses such as a method using a toner, a method using a plurality of intermediate transfer members, and a method using intermediate color toner.

In addition, in recent years, in accordance with demands from the market, color image forming apparatuses, such as color copiers and color printers, have increased in number, but image forming apparatuses can only form monocolor images. It may be.
When a developer is used as an image forming material used in such an image forming apparatus, the developer is not limited to a two-component developer but may be a one-component developer.

  The image forming apparatus may not be a copier, a printer, and a facsimile machine, but may be a single unit thereof, or may be a multi-function machine of another combination such as a copier and printer. .

  The effects described in the embodiments of the present invention are only the most preferable effects resulting from the present invention, and the effects of the present invention are limited to those described in the embodiments of the present invention. is not.

DESCRIPTION OF SYMBOLS 11 Endless belt 30 Detection means 33, 72, 74, 75 Several rollers 33, 72, 74 Other rollers 42 Small diameter part 43 Part contact | abutted to belt 44 Inclination part 75 Opposite roller 100 Image forming apparatus D1, D2, D3 , D4 Roller diameter L1, L2, L3, L4 Width of small diameter portion MA Area where image is carried on endless belt

JP 2008-185960 A JP-A-2005-338700 JP 2001-318538 A Japanese Patent No. 4051858

Claims (9)

An endless belt stretched around a plurality of rollers;
Detecting means for optically detecting an image on the belt;
The plurality of rollers includes an opposing roller facing the detection means across the belt, and other rollers,
At least the counter roller of the plurality of rollers has a small-diameter portion having a smaller diameter than other portions corresponding to a region in which the image detected by the detecting unit is carried in the width direction of the belt. . The image forming apparatus according to claim 1.
In the width direction, the width of the small-diameter portion is equal to or larger than the width of the detection area of the detection unit. The image forming apparatus according to claim 1 or 2,
A plurality of rollers having the small diameter portion among the plurality of rollers;
2. An image forming apparatus according to claim 1, wherein in the width direction, the width of the small diameter portion is made different between the rollers having the same small diameter portion. The image forming apparatus according to any one of claims 1 to 3,
A plurality of rollers having the small diameter portion among the plurality of rollers;
In the width direction, an image forming apparatus characterized in that a width of the small diameter portion provided in the counter roller is smaller than a width of the small diameter portion provided in another roller. The image forming apparatus according to any one of claims 1 to 4,
A plurality of rollers having the small diameter portion among the plurality of rollers;
An image forming apparatus, wherein a width of the small-diameter portion provided in a roller different from the facing roller in the width direction is set according to a diameter of the roller. The image forming apparatus according to claim 5.
A plurality of rollers having the small diameter portion among the plurality of rollers;
The image forming apparatus according to claim 1, wherein the width of the small-diameter portion provided in a roller different from the facing roller in the width direction is set larger as the diameter of the roller is smaller. The image forming apparatus according to any one of claims 1 to 6,
Among the plurality of rollers, the roller having the small diameter portion is formed continuously between the portion in contact with the belt and the small diameter portion in the width direction and has a diameter toward the small diameter portion. An image forming apparatus having an inclined portion that gradually decreases. The image forming apparatus according to any one of claims 1 to 7,
Of the plurality of rollers, a roller different from the counter roller is determined whether or not to provide the small diameter portion on condition that the diameter is large, and when the diameter is large, the roller does not have the small diameter portion. An image forming apparatus. The image forming apparatus according to any one of claims 1 to 8,
Of the plurality of rollers, a roller different from the opposing roller is determined as to whether or not the small diameter portion is provided on the condition of the surface elasticity, and when the surface elasticity is large, the roller does not have the small diameter portion. An image forming apparatus.

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